Crystal oscillator



prfifi 21, 136. A. H. TAYLOR I fi 'v CRYSTAL OSCILLATOR Filed April' 24, 1954 39 w *W I I'I mm Wk w M FM INVENTOR ATTO NEY Patented Apr. 21, 1936 UNITED STATES PATENT OFFICE 11 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) This invention relates broadly to electron tube oscillation generators, and more particularly to a method of and means for compensating for the tendency of an oscillation generator to produce 5 oscillations of varying frequency and varying amplitude as the potential of the source of anode potential of the generator is varied.

For control of frequency to an extremely high order of precision, as for example a few parts in 1G a million, best practice uses a piezo electrically controlled oscillator, the crystal in the circuit being maintained at a constant temperature and worked at rather low power. In such case, how ever, considerable care has to be taken to provide constant voltage generators since even a piezo electrically controlled circuit will change its frequency as much as 30 to 100 parts in a million if any considerable change in the plate voltage applied to the piezo electrically controlled oscil- 00 lator happens to take place. It is not only desirable but increasingly essential to hold the output of the oscillator constant and at the same time to hold its frequency constant in spite of accidentalvariations in plate voltage. It is possible to use the tetrode, such as is ordinarily used as a shield grid tube, as a piezo electrically controlled oscillator provided the shield grid is not by-passed to filament but is rather fed at suitable voltage through a radio frequency choke. A study of the frequency variations in such an oscillator shows that the frequency increases when the plate voltage is increased and decreases when the plate voltage is decreased. The same law of action holds for variations on the so-called screen electrode which is now no longer used as a screen. From the above it is seen that with a tetrode having its cathode, grid and anode connected so as to produce oscillations, the tendency of a change in anode potential to produce a change in the amplitude and frequency of the generated oscillations may be offset by applying to the grid adjacent to the anode a potential inversely pro-- portional to the varying potential applied to the anode and leaving said grid adjacent the anode free to assume whatradio frequency potential that it will.

.Thus an object of this invention is to provide a. method of and an apparatus for automatically maintaining the frequency of oscillation of an oscillation generator substantially constant irrespective of changes of potential of the source of energy for energizing said generator.

Another object of this invention is to provide a method of and an apparatus for automatically controlling the potential of the grid adjacent the of energy for energizing said generator. O

Other and further objects of my invention will be apparent from the specification and claims following when taken in connection with the accompanying drawing in which the figure shows diagrammatically one form of circuit incorporating the invention.

In the drawing, I is a tetrode or a thermionic tube having cathode 2, control grid 3, anode 4, and an outer grid or shield grid 20. The cathode 2, control grid 3 and anode l are connected with external circuit connections so as to comprise a conventional type of piezo electric crystal oscillator in which a piezo electric crystal 5 is connected across an inductance 6 which is in turn connected between the cathode 2 and control grid' 3, and a battery or other source of anode potential I2 is connected in series with a parallel resonant inductance l and condenser 8 between the plate or anode 4 of the tube and the cathode 2. The sliding contact 9 connected to anode 4 may be varied in position along the inductance 1 so that all or any desired portion of the inductance may be included in the anode current path. A condenser II is connected from the cathode 2 to inductance 1 so as to bypass the battery or other source of potential l2. A slid ing contact l0 adapted to be adjusted to any desired position along inductance l constitutes, together with ground 38, the output terminals of the oscillation generator. 40

The oscillation generator described above without element 20 and its associated circuit is a conventional piezo electrically controlled oscillator in which a change of potential of a source of anode potential !2 may cause the output frequency delivered at H) to vary both in frequency and in amplitude. In order to compensate for the tendency of the above described oscillation generator to change its frequency of oscillation with a change of the potential of source l2, a positive potential, which varies in value substantially inversely as the value of the potential applied to anode 4, is impressed upon the outer grid 20. This potential is controlled as an inverse function of the current flowing in the anode cir- 55 cuit of the triode I3 having cathode I4, control electrode I5 and anode I6. The control electrode I5 is connected by way of condenser I1 and slider II] to the inductance I so that the potential of the grid or control electrode I5 is controlled in accordance with the high frequency potential flowing in the tuned circuit comprising inductance 1 and capacity 8. The grid or control electrode I5 is connected by way of radio frequency choke coil I8 and slider 39 to a point on battery |9,.the positive terminal of which is connected to the cathode I4. The anode I6 is connected by way of the resistance 22 and battery or other source of anode potential 23 to cathode I4. Anode I6 is also connected by way of the radio frequency choke 2| to the outer grid 20 of tetrode I.

The biasing potential applied to grid I5 by battery I9 is of such a value that little current flows in the anode circuit of the triode I3 when there is no high frequency superimposed upon grid I5. However, when a high frequency is impressed upon grid I 5 due to the fact that the tetrode I is producing oscillations in its circuits under control of the piezo electric crystal 5, it is seen that the anode current of tube I3 increases, producing an increased voltage drop across the resistance 22, which is included in the circuit of anode I6.

With the tetrode connected as hereinbefore described and with the regulating tube or triode I3 having its input circuit energized from the output of tube I, it is seen that a change in the amplitude of the oscillations in the output circuit of tube I will cause a corresponding change in the current in the anode circuit of triode I3 and resistance 22. This change in the current flowing in resistance 22 causes a change in the potential drop thereacross, resulting in a drop of the steady value of the potential applied to grid 20. This change of potential applied to grid 20 tends to reduce the amplitude of the output oscillations of the tube I and thereby prevents the frequency generated by tube I from shifting due to a change in the amplitude of the oscillations generated. The output circuit of oscillation generator tube I is also connected by way of condenser 24 to energize the input of tetrode 25 which is connected as a shield grid amplifier, with its shield grid 28 bypassed to the cathode 26 by way of condenser 32. The anode 29 of shield grid tube 25 is connected by way of inductance 34 to the positive potential terminal of the battery 23; the shield grid 28 is connected by way of resistance 3| to the positive potential terminal of battery 23; the control grid electrode 21 is connected by way of radio frequency choke 39 to a point on the battery I9 by way of slider 45. The biasing potential applied to grid 21 by means of battery I9 is of such a value as to cause the tetrode 25 to amplify the input oscillation efii ciently. The inductance 34 is shunted by a variable condenser 35 and together inductance 34 and condenser 35 form a tuned output circuit for the amplifier tube 25, which circuit may be tuned to the fundamental frequency generated in tube I or any desired appropriate harmonic thereof. A lead 3'! which may be connected to the input of a further amplifier or to an antenna system is connected to inductance 34 by means of a slider 36.

The cathodes of oscillation generating tetrode I, the regulating triode I3 and the amplifying tetrode 25 are all shown as filamentary cathodes and as being energized from a single source of cathode potential connected to leads 4| and 42.

but it is to be understood that heater types of tubes employing unipotential cathodes may also be used. Separate sources of anode potential are shown energizing the anode circuit of tetrode I and the anode circuits of tubes I3 and 25 but it is to be understood that the same source of potential could be used in lieu of the separate sources I2 and 23, provided the necessary changes are made in the values of the circuit constants. The grid 20 is shown connected by way of radio frequency choke coils 2| directly to anode I6 of regulating tube or triode I3, but this connection need not be made directly to the anode. The connection to the grid 20 could be made at any desired point on the resistance 22, in which case it might be desirable to connect said grid to a slider that could be selectively varied along the resistance 22.

It will be understood that the above description and accompanying drawing comprehend only the general and preferred embodiment of my invention, and that various changes in construction, proportion and arrangement of parts may be made within the scope of the appended claims without sacrificing any of the advantages of my invention.

The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without the payment of any royalties therefor.

I claim:

1. A source of high frequency oscillations comprising an electron tube having a cathode, an anode, a control grid and an auxiliary grid element, frequency determining means connected between said control grid element and said cathode, a tuned output circuit and a source of anode potential connected in series between said anode and said cathode, and means for applying to said auxiliary grid element a potential having a component which varies inversely as the high frequency component of current in said tuned output circuit.

2. A source of high frequency oscillations comprising an electron tube having a cathode, an anode and a control grid, a piezo electric crystal operatively associated with said tube between said cathode and said grid, a source of anode potential and a tuned resonant circuit connected between said cathode and anode, and means for maintaining the output of said tube substantially constant notwithstanding variations of potential of said source of anode potential comprising a potential gradient controlling electrode within said tube between said anode and the other electrodes, and means for applying to said electrode a positive potential having a component which varies inversely as the potential of said anode.

3. An electric system comprising, in combination, a thermionic tube having a cathode, a control electrode, and an anode, an electromechanical vibrator connected between said cathode and control electrode forming an input circuit, a source of anode potential, and a tuned resonant circuit connected between said cathode and anode forming an output circuit, said input and output circuits being substantially uncoupled together except through the tube, a grid-like electrode in said tube between the electrodes contained in the input circuit and the anode, and means for applying to said grid-like electrode a positive potential having a component which varies inversely as the amplitude of the oscillation in said output circuit.

4. An electric system comprising, in combination. an amplifying relay having a cathode. a control grid electrode, a grid-like auxiliary electrode and an anode, a source of anode potential, a tuned circuit, a piezo-electric body, an inductance, said piezo electric body and said inductance being connected in parallel between said cathode and said control grid electrode, said tuned circuit and said source of anode potential being connected in series between said cathode and said anode, and means for applying to said grid-like auxiliary electrode a positive potential having a component which varies inversely as the potential of said source of anode potential whereby the frequency of the oscillations generated in said sys tem is substantially independent of variations of potential of said source of anode potential.

5. In combination, an electron tube having oscillation generating electrodes and an auxiliary electrode, a source of potential and circuits: interconnecting said oscillation generating electrodes for generating and sustaining oscillations therein and means for compensating for the tendency of the oscillations generated by said oscillation generating electrodes to change in frequency with a change in amplitude thereof comprising an arrangement for impressing a potential on said auxiliary electrode having a component which varies inversely as the amplitude of the oscillations generated.

6. In an oscillation generating system comp-rising an electron tub-e having a cathode, a control grid, an anode and an additional element, the cathode, control grid and anode of which constitute with their external circuits an oscillation generator, the method of compensating for changes in the frequency of oscillation resulting from variations in potential of the source of anode potential which comprises applying a positive potential to said additional element and varying the potential applied to said additional element inversely as the potential of the source of anode potential varies.

'7. In an oscillation generating system comprising an electron tube having a cathode, a control grid, an anode and an additional element, a piezo electric crystal connected between said cathode and said control grid, a resonant circuit and a source of anode potential connected between said anode and said cathode, the method of compensating for changes in the frequency of oscillation resulting from variations in potential of the source of anode potential which comprises applying to said additional element a positive potential and varying the value of said potential inversely proportional to the potential applied to said anode.

8. In an oscillating electron tube circuit having an electron tube containing a cathode, a grid electrode, and two spaced electrodes surrounding said cathode and grid. electrode with a piezo electric crystal included in circuit between said cathode and grid electrode and a tuned resonant section and a source of potential included in a series circuit between the outermost of said spaced electrodes and said cathode, the method of avoiding frequency modulation resulting from changes of potential of said source of potential which cornprises utilizing the generated oscillations tocontrol the flow of a uni-directional electric current in accordance with the amplitude of said oscillations and applying a positive potential to the innermost of said. spaced electrodes which varies in value inversely as said uni-directional current.

9. An electric system comprising, in combination, an amplifying relay having a cathode, an inner grid electrode, an outer grid electrode, and an anode, a piezo electriccrystal and an inductance connected in parallel between said cathode and said inner grid, a tuned resonant circuit and a source of potential connected in series between said anode and said cathode, a second amplifying relay having a cathode, an anode and a control electrode, means for normally maintaining the control electrode of said second amplifying relay negatively charged with respect to the cathode, an alternatingcurrent path from a point in said tuned resonant circuit to said control electrode, a resistance and a source of anode potential connected in series between the anode and cathode of said second amplifying relay, and a high frequency choke connected between the anode of said second amplifying relay and the outer grid of said first amplifying relay.

10. A source of high frequency energy comprising a thermionic tube havng a cathode, an anode, a grid control electrode and a potential gradient controlling electrode, a. frequency determining device connected between said grid control electrode and said cathode, a resonant impedance included in circuit between said anode and said cathode, a first and second amplifying relay having their input circuits connected for parallel energization by the oscillations flowing in said tuned impedance, a resistance and a source of potential connected in series in the output circuit of the first of said relays and an inductive impedance connected between said potential gradient controlling electrode and a point on said resistance.

11. A source of high frequency energy in accordance with claim 10 including a tuned output circuit for the second of said relays and means for electrically isolating said tuned output circuit from the circuits of said thermionic tube and said first amplifying relay.

ALBERT I-I. TAYLOR. 

